Image forming apparatus and method



c. F. CARLSON 3,182,591

May 11, 1965 IMAGE FORMING APPARATUS AND METHOD Filed May 22, 1963 4 Sheets-Sheet 1 FIG. 1

INVENTOR. Chester E Carlson BYk ATTORNEY May 11, 1965 c. F. CARLSON IMAGE FORMING APPARATUS AND METHOD 4 Sheets-Sheet 2 Filed May 22, 1965 QC. HIGH VOLTAGE FIG. 2

mvmon Chester F. Carlson ATTORNEY C. F. CARLSON IMAGE FORMING APPARATUS AND METHOD May 11, 1965 Filed May 22, 1963 4 Sheets-Sheet 3 DC HIGH VOLTAGE v I fill! I I I INVENTOR.

Chester E Carlson BY ATTORNEY y 11, 1965 c. F. CARLSON 3,182,591 IMAGE FORMING APPARATUS AND METHOD Filed May 22, 1963 4 Sheets-Sheet 4 7g 75 I 4 LINE SELECTION EWT E'S 1 2 3 4 5 6 7 8 7s 7' GATES CHARACTER REGISTER -77 COMPARISON VOLTAGE 72 CIRCUIT AMPLIFIERS CHARACTER COUNTER =9 7 Q 0 Q 7 O Q ELECTRODES o O 52 8 O O '9 t; Q 0 was ASSEMBLY I G p 5 o c G a 63 G 5 p 8 O o o MAGNETIC SPOTS G p Q 0 o (ONE PER 2 4 v CHARACTER) 79 G v I 64A c; P O 642@ 30 G I Q 5 62 U Ii- !IIII" FIG. 5

mvmon Chester E Carlson 4 ATTORNEY United States Patent 3 182 591 IMAGE FORMING APPARATUS AND METHOD Chester F. Carlson, Pittsford, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed May 22, 1963, Ser. No. 284,283 6 Claims. (Cl. 101-426) This invention relates to the electric recording of characters, and to the application of such recording to electrostatic image processes.

In the more familiar aspects of electrostatic recording it is usual to first form an electrostatic image, for example, by the combined action of electric field and exposure to light. Such an image is then developed or made visible by the deposition of electrostatically attractable powder or other finely divided material, as is now conventional. I have found, however, that certain images, like alphanumeric or character images, may advantageously be formed in the absence of exposure to an existing original. Thus, I have found that an electrostatic image can be formed on a suitable insulator by applying an electric field from an adjacent member and that this means of image formation is virtually instantaneous in its response and is well adapted for the recording of conventional coded electric signals including high-speed computer output. One such form of recording is disclosed in my co-pending application S.N. 532,534, filed September 6, 1955, which in turn is a continuation of my earlier application S.N. 307,120, filed August 29, 1952, and now abandoned. The present invention thus relates to image formation in response to an electric signal which need not be light responsive, and to the formation of an image that is immediately visible. This application is a continuation-inpart of my co-pending application S.N. 687,698, filed October 2, 1957, and now abandoned, which is in turn a continuation-in-part of application S.N. 532,534, filed September 6, 1955.

Now in accordance with the present invention an immediately visible record corresponding to an electric impulse is formed by placing an insulating layer having its surface coated with a releasable electroscopic material in face-to-face relationship with an image receiving surface and applying an intense electric field, optionally in the form of an electric pulse, in image configuration so as to transfer to the image receiving surface a body of electroscopic material in corresponding image configuration. Illustratively, a suitable powder carrying insulating layer, such as paper or plastic is dusted with an electrically charged, black or colored, finely divided powder and is placed in face-to-face relationship with an image receiving layer such as, for example, a web or sheet of paper. An alphanumeric character is placed behind one of the layers as, for example, by presenting a shaped character face of conductive material behind such surface, and a pulse of electric field or potential is imparted to the character face with relation to a suitable electrode behind the opposite surface, the polarity and voltage being such as to move the powder toward or transfer its afiinity to the image receiving surface. Preferably an initial electric potential or stress is applied below the threshold level of image transfer whereby transfer can then be accomplished by the application of a relatively lower potential electric pulse between the character face and the counterelectrode.

It is to be realized that an electric pulse of the proper polarity may be applied either behind an insulating powder carrying layer or behind the insulating image receiving layer. In the presently preferred embodiment of the invention, however, it is found to be advantageous to employ an insulating powder carrying layer with the character 3,182,591 Patented May 11, 1965 behind this layer, thus permitting the use of mildly conductive ordinary paper as a consumable image receiving or print support layer. The invention will, therefore, be described with particular reference to such an insulating powder carrying layer, with the understanding that this basis of description is for purposes of simplicity of illustration rather than as a limitation of the scope of the invention.

Although it is not intended to limit this invention to any paricular theory of operation, it is thought that a brief discussion of the present understanding of the invention may be helpful to a full description. It is presently believed that it is necessary to apply a sufiiciently high electric potential between the character face and the back of the powder carrying layer to cause actual transfer of electric charge across a narrow gap to the back of the powder carrying layer. When air is employed as the fluid in the gap transfer is believed to be the result of air ionization and to be caused by the extremely high velocity imparted to the few ambient electrons normally existing in the atmosphere, whereby the electrons achieve in their means free path a velocity sufiicient to cause them, upon collision with gas molecules to produce positive ions and additional electrons. As a result there will be formed from a first electron an increasing numbe rof ions directly as a consequence of this high velocity. As the positive ions so produced reach the negative electrode or surface they release further electrons from this surface to continue the process. Other fluids including gases and liquids may be used although the following description is made in terms of air.

The image formation of the present invention occurs when an electrostatic charge in the configuration of the character face is laid down on the back of the powder carrying layer as a result of a short gaseous electric discharge and as a result of which the afiinity of the powder layer in this area is transferred to the image receiving layer. To achieve this result the air gap between the character face and the back of the image receiving layer must be sufficiently long to allow electron avalanches to form by repeated ionizing collisions of electrons with neutral atoms or molecules. This requires a gap of two microns or more. Below this distance there are insufiicient gas molecules encountered by the initial electrons in their travel across the gap. For practical reasons, to provide clearance between relatively moving parts, the spacing is preferably at least 25 microns, or one-thousandth of an inch. The spacing should not normally exceed 250 microns or 10 mils, and for best images should not exceed about microns, or 5 mils, as above this gas length the images tend to become indistinct due to spreading of the change and electrical treeing or the formation of so-called Lichtenberg figures.

The record requirement is that the voltage of the pulse be sufficient to produce an electric field in the gap which will produce gas ionization and avalanche formation during the brief interval of the pulse. This will vary with the length of the gap, the wave shape of the pulse, and the length of the pulse. For the longer gaps the overall volt age must be higher, but the field strength required in the air gap is less. Thus, for air gaps of 125 microns or greater a field strength of 6 volts per micron of air gap length is about the minimum field for image production with a square of a few microseconds, while for a 25 micron gap the minimum field strength required may be 20 volts per micron. The maximum field strength which will product distinct images is approximately twice the minimum. The total voltage required will vary with the thickness and dielectric constants of the layers interposed between the electrodes and may range from about 600 volts to 2,000.

Third requirement is that the powder carrying layer be an insulator. A fourth requirement, for continuous recording equipment where there is relative motion between the character face and the powder carrying layer is that the pulse be of sufficiently short duration so that the motion of the character during the pulse interval is only a small percentage, preferably less than 10% of the height of the character, to prevent the production of a smeared-out image.

The general nature of the invention having been set J FIG. 4 is a diagrammatic view of a simple high-speed printing device of the type illustrated in FIGS. 2 and 3 employing a predusted image-forming surface; and

FIG. 5 is a diagrammatic representation of electrode and circuitry arrangement useful in the invention.

Referring now to the figures, FIG. 1 illustrates a simple apparatus embodying the invention and useful for applying code data, emblems, reference numerals, letters and symbols, of other alphanumeric and like data to a suitable sheet material including paper, cloth, metal, plastic and the like. The data and information may, if desired, be original data applied to a previously blank image receiving surface or may be selectively overprinted or interlineated data applied to a surface already containing appropriate information or design. Thus, for example, the apparatus is useful for producing original information and data on a sheet or web of paper or business forms, for applying designs, or for imparting information in the margins of already imprinted or image bearing material or photographic film for identification or the like.

In FIG. 1 there is illustrated a copy sheet 11 such as a sheet of paper or the like which is positioned and adapted to receive the image. This sheet is positioned on a conductive base 14 and an insulating developer sheet 12, coated uniformly with electrostatically adhering resinous powder 15, is laid powdered surface down on the copy sheet. A type slug E3 or similar alphanumeric character image preferably of metal or like electrically conductive material is placed in light contact with the back of the developer sheet 12 or spaced a few thousandths of an inch therefrom. For simplicity of operation it is frequently desirable to place the type slug in virtual contact with the developer sheet 12 and when this is done it is critically necessary to assure that the two surfaces are in extremely light contact. Virtual contact for the purpose of this description is defined as the condition of close proximity existing when one of the surfaces rests lightly and loosely against the other in loose contact, generally producing a spacing of about 2 microns at all except remotely distributed points of contact. This condition is to be distinguished from a condition of firm contact between the two surfaces in which case the spacing is in the order of about 1 micron, and also should be distinguished from a condition of pressure contact between the two surfaces at which the spacing is in the order of a fraction of 1 micron. For effective operation of this invention it has been found necessary to maintain spacing between the twosurfaces at about 2 microns or higher, and preferably the two surfaces are spaced apart at a distance in the order of about to 75 microns.

For electrical impulsing of the type slug alternative operating circuits are shown, either or both of which can be used for recording. The first operating circuit is connected to type slug 13 through the front contacts of switch 9. a Battery 16 thereby applies a bias to the type slug making it negative with respect to conductive base 14, this bias field being insufficient to transfer the developer material from layer 12 to layer 11. A second battery 18 is connected through switch 17 in parallel with a resistor 19 and in series with battery 16. When switch key 17 is closed the potential of battery 18 is added to the potential of battery l'to apply a pulse in addition to the potential applied between conductive members l3 and 14. The potentials produced by batteries 16 and 18 are so selected that should the potential of battery 16 be insufiicient to transfer the potential from one surface to the other when the copy sheet and developer are placed lightly together then the total poten tial of batteries 16' and 18 is sufficient to produce such developer transfer. Potentials of about 300 volts for battery 16 and 500 volts for battery 18 have been found satisfactory.

A second key-operated circuit is illustrated in FIG. 1 to apply a pulse to the type face 13. This circuit is connected to type slug 13 by closing the back contact of switch 9. The second circuit comprises a transformer or spark coil 23 with a high voltage secondary connected between type slug 13 and ground, and hence to base 14 which is also grounded. The primary circuit of the transformer includes a switch 29 having a key-operated common contact arm and front and back contacts for cooperation therewith, a condenser 21 and a battery 22. The contact arm of the switch is connected to one terminal of the condenser, the other condenser terminal being connected to one end of the transformer primary winding and to one terminal of battery 22.

When the switch is operated to engage the arm and front contact a circuit is completed to charge condenser 21 from battery 22. When the switch arm is released it opens the charging circuit and then engages the back contact which is connected to the remaining end of the primary winding, thereby closing a discharge circuit for condenser 21 through the primary. Discharge of the condenser through the primary induces a high voltage pulse in the secondary winding and this pulse is applied to the type face 13. The polarity of battery 22 is arranged to produce a negative pulse on type face 13, if the powder 15 has a negative charge, and hence a powder image is transferred to sheet 11 by the pulse. Due to the damping of oscillations only the first pulse from the transformer reaches a sufliciently high peak of potential to be effective in transferring powder. Succeeding oscillations of alternating polarity are ineffective since the peak potential falls off rapidly with each half cycle. Thus, the second pulse, which is of opposite polarity to the transfer pulse is lower in peak voltage and does not transfer back any powder. It has been found, morea over, that even a complete reversal of field to the maximum voltage will not transfer all the powder back. Image transfer operating from a pulse as short as a' few microseconds has produced good quality character images.

The developer sheet 12 may be any suitable thin insulating material such as a dried paper or plastic web coated with a releasable transferable charged powder material. Desirably', powder may be coated on a sheet of paper by brushing it on or by cascading across the paper surface of the powder itself or a powder carrier mixture such as is disclosed in Walkup and Wise patent, US. 2,638,416. 'Powder of a positive or negative polarity may be deposited on the developer sheet 12, but it has been found generally that xerographic developers which are most readily available and useful in this invention generally acquire a negative electric charge in contact with most surfaces. Thus, sheet 12 may be drypaper, dry cloth or a plastic film material such as Mylar, polystyrene, cellulose acetate or other insulating sheet material, and the developer powder may be a powder of the type disclosed in the hereinabove Walkup and Wise patent, or may be such other powder as is conventionally used in the art of xerography. The application of a negative polarity pulse to the type slug produces image transfer.

Developer sheet 12 is of insulating material so that an electric charge from type face 13 may be deposited on the surface and may retain its charge configuration until transfer of the powder image is effected. Transfer of the affinity of the powder to the copy sheet 11 is believed to take place almost simultaneously with the electric pulse but if the conductivity of developer sheet 12 is sufiicient to allow spreading of the area of charge before separation of sheets 11 and 12 some loss in definition in the powder image may take place. Therefore, it is preferred that the sheet 12 be sufiiciently insulating to retain a sharply defined electric charge image until the sheets are separated. This time will depend upon conditions or" use and may vary from a fraction of a second to several seconds for various applications.

In FIG. 2 is illustrated an output recorder adapted to produce a high speed instantaneously developed image in response to a timed input and a coded signal from a suitable pulse source. This output recorder is adapted to record the output of a computer, a signal receiving circuit or other source of a coded electric signal or may be operated from a memory storage device such as, for example, a magnetic tape or the like. It will be appreciated, however, that the circuit illustrated is by way of example only, and that other circuit arrangements can be used with the mechanical system disclosed.

Corresponding to the device illustrated in FIG. 1, the recording means or the image forming member is a rotatable conductive cylindrical printing drum having raised alphanumeric character faces on its periphery.

The printing cylinder 31) includes a plurality of rings or columns of alphanumeric type faces arranged around the periphery of the drum. These columns generally have a sequence such as numbers from 0 to 9, or a sequence such as the letters of the alphabet or the like. Desirably, the character rings may be in a series along the length of the cylinder corresponding to the length of a line of printing to be produced in image form along the image receiving surface. Thus, for example, each of the rings may consist of a separate character Wheel mechanically joined to the adjacent ring or if desired a single conductive cylinder may be employed with a plurality of conductively joined character rings as shown in FIG. 3. The character faces all lie in a cylindrical imaginary surface slightly above the drum surface and are spaced at an identical radius from an axle on which the cylinder may be rotated. When the electrode assembly 36 is separately pulsed and the cylinder is suitably grounded or electrically biased, the character wheels may be electrically joined as well as mechanically joined. However, greater flexibility of operation may sometimes be achieved by electrical separation between the character wheel-s, whereby the separate whels may be successively biased or activated for printing in successive columns.

The cylindrical drum 30 is disposed inside an independently rotatable insulating cylinder 32 of dry paper, plastic, or other suitable insulating material, which is supported by freely rotating end support discs 33 (FIG. 3) at a spaced distance of several thousandths of an inch above the character faces. If desired, the cylinder 32 may be smooth but it has been found to be preferably to employ a slightly grained or fibrous outer surface in order to improve the deposition and retention of the developer powder thereon.

Positioned adjacent to the surface of cylinder 32 and adapted to feed an image web or copy sheet 11 of dried paper or other sheet insulating material against the cylinder surface are suitable paper or web feed means. Such feed means may include, for example, a supply roll 42, feeding a web of image receiving material 11 either to a suitable take-up roll or around a web drive roll 48 from whence it passes to a copy storage or distribution location (not shown). Guide rolls 26 are suitably positioned to guide the moving paper into contact with the cylinder surface and to direct it in a path through the computer output recorder. A roll 26A holds the web against drive roll 48 to prevent slippage. An electrically heated hot plate 43 bears against the back of the web between the printing cylinder and drive roll 48 to fuse the powder images to the web and thereby produce a permanent record.

An electrode 36 is positioned opposite each ring or column of characters on the face of cylinder 30 and directly behind the web 11 as it passes in contact with pow der cylinder 32. The faces of the electrodes are curved to conform to the cylindrical shape of the web at this point.

The electrode energizing system for only one of the columns or rings of characters is shown in FIG. 2, the electrodes and circuits for the other columns being similar. For the circuit illustrated electrode 36 is biased by a battery 16 through adjustable potentiometer 116 to raise it to a potential slightly below that required for recording. The polarity of the electrode is opposite to the polarity of charge which is on the powder coating of cylinder 32. In the present illustration the powder carries a negative charge and electrode 36 is given a positive potential in relation to ground by battery 16, the negative terminal of which is grounded through resistance 118. A capacitor 117 is connected across potentiometer 116.

A triode 119 has its cathode connected to resistance 118 and to electrode 36 through capacitor 117. The anode is connected through battery 126 to ground so that when triode 119 is made momentarily conducting the potential of battery 120 is applied across resistance 118 to add this potential to the fixed potential applied to electrode 36 by battery 16, and thereby to produce an electric field between electrode 36 and a character face of cylinder 30 sufiiciently high to transfer a powder image of the character to web 11.

The grid of triode 119 is normally biased to cut-off potential and this bias is reduced for a short interval whenever a timed recording signal is received from the signal source. The bias is reduced for only a short interval so that the motion of cylinder 30 is insufiicient to cause blurring during the period of a recording pulse. For rapidly operating equipment the pulse length may be only a few microseconds.

The timed input pulse circuit controlling the grid of triode 119 may be similar to that shown in my co-pending application Serial No. 532,534, filed September 6, 1955, for Electrostatic Recording of Images, or any of a variety of pulse timing and distributing circuits well known in the art. Thus, as shown in FIG. 2, a binary signal representing the letter D may be received over input circuit 121 and stored in the appropriate position in the timed input pulse circuit 122. An iron disc 35 which is mounted on the same shaft as drum 30 has a series of slots or notches 124 around its edge in positions corresponding to the spacing of the character faces and a stationery pick-up magnet 125 is positioned at the edge of the disc to supply a pulse over conductors 123 to the pulsing circuit 122 as each slot passes the magnet. Thus, when a character signal from conductor 121 has been stored in circuit 122 the pulses from chrcuit 123 are counted by circuit 122 until the appropriate character comes opposite electrode 36 at which time the grid potential of triode 119 is modified by circuit 122 to produce a recording pulse for the character.

A second pick-up magnet 127 is positioned to transmit a pulse over a circuit 128 at the completion of each cycle of rotation of the drum when slot 126 passes the gap of the magnet to initiate storage of another character signal in circuit 122 for recording on the next cycle.

Suitably mounted and positioned adjacent to the surface of cylinder 32 is a development material deposi tion device such as, for example, a rotating brush 40 or 2 the like adapted to deposit powder material on the cylinder by means of bringing to the cylinder surface charged powder particles either supported on the brush fibersor otherwise carried to the surface. For example, a developer powder 27 is placed in a feed bin 28 and is carried slowly to the brush it? by a slow-moving feed drum 2h. Suitable drive mechanism such as a worm gear 49 operated by a motor 50 may operate the feed drum, optionally working from the same drive shaft as the drive means for brush 40.

Optionally mounted on character cylinder 3h is a charge neutralizing device such as, for example, a corona discharge wire 38 operably connected to a suitable high voltage source and adapted to apply uniform charge potential to the inner surface of cylinder 32, thus erasing any residual electrical image on said surface.

As shown in FIG. 3, the cylinder 30 is rotatable in dependently of cylinder 32 and may be suitably driven and synchronized by a motor 3% in coordination with suitable synchronizing means. Simultaneously, the outer cylinder may be rotated on bearings 31 and may be independently driven or, preferably dragged by web 11. In the preferred method of operation, cylinder 30 will be rotated one time for each movement or advance of one line of printed information on web 11.

In FIG. 4 is illustrated a modified device employing a pro-dusted developer web 52 passing from a supply roll 53 around a printing cylinder 30 which is comparable to the printing cylinder of FIG. 3. This pre-dusted web may, for example, be a web of insulating paper or plastic material, preferably grained or fibrous, which prior to insertion in the apparatus has been coated with a releasable electrostatically adhering powder material. The Web is positioned to pass by a cleaning and discharging brush 54 bearing against the back surface and thence between a corona charging electrode 55 and a grounded backing shoe 57. The web then passes around the cylinder 30 with its edges resting on support discs 33 by which it is spaced a few thousandths of an inch from the character faces. The web is then wound up on take-up roll 56 which continuously applies a slight tension to the web 52.

The image-forming station around the circumference of the cylinder is an electrode system generally designated 36 as in FIG. 2. Passing between the developer web 52 and this electrode system is a suitable copy sheet or web 58 optionally passing from a feed roll 59 around guide rollers 60. After passing against the cylinder the copy web 58 may be processed through a fusing oven 43 and ther passed over a drive roller in the same manner as in F1 2.

In FIG. 5 is illustrated certain electrode and circuitry arrangements useful according to the invention and particularly useful in conjunction with the high speed printing device such as illustrated in FIGS. 2 or 4. According to these figures the recording device includes a motor driven rotatable drum 61 like the drum of the device in FIG. 2 having a plurality of rings with raised character faces 62 optionally arranged as numbers 0 to 9 and letters of the alphabet from A to Z. One ring of characters is provided for each column of recording and the cylinder extends generally across the printed page. At the ends of the drum are attached a pair of indexing discs 63 and 65. Disc 63 at one end carries a single magnetic spot 64 for the location and counting of revolutions and disc 65 at the other end carries a plurality of magnetic spots 64a for the location ofcharacters within a revolution. One such character location spot 64a is positioned in line with each row of characters. A revolution reading coil or head 79 is mounted adjacent to the path of magnetic spot 64 and a second character reading head is mounted adjacent to the path of the character magnetic spots 64a.

Adjacent to the circumference of the cylinder 61 at an ancer 8 impulse station "are a plurality of electrodes 66 corresponding to the electrode assemblage generally designated 36 in FIG. 2. One of such electrodes 66 is positioned opposite each of the character rings and is operably connected to electronic circuitry to provide an impulse voltage at a timed instant when a character is to be recorded. A web assembly comprising a copy web 58 and a developer web 52 or alternatively the insulating cylinder 32 of FIG. 2 is adapted to be fed between the cylinder 61 and the electrode assembly.

In operation when a selected character passes over a chosen electrode the electrode is subjected to a triggered pulse. The manner of sequentially selecting the proper character ring and the particular character therein involves the use of digital computer techniques. Appropriate ring counters, delay devices and the'like may be employed. To illustrate one form of circuitry, the input from the'computer or memory storage device is fed into a character register 71, thence to a comparison circuit 72 with control operation from a character counter 73. Simultaneously a revolution counter 74 feeds to a line selection matrix 75 in coordination with a signal from the comparison circuit 72. With each of the electrodes 66 is associated a voltage amplifier 77 energized by a gate 78 which is selectively triggered by the comparison circuit 72 and the line selection matrix 75.

In use and operation the electrodes are individually triggered in response to the signal from the revolution counter and character counter combined with a voltage pulse from the computer output or memory device output. Thus, the comparison circuit and revolution counter in conjunction operate the gates '78 whereby a pulse input from the computer output produces a triggering impulse to the corresponding electrode d6;

The apparatus represented in FIG. 5 may be employed for sequential character formation. In such an arrangement the revolution counter sequential opens first one and then the next of the gates, for sequential character formation, and when so employed the rows of characters on the cylinder and, if necessary, the electrode assembly, desirably are skewed with respect to horizontal direction on the web assembly so as to correct for continuous vertical motion of the Web assembly through the device. One such skewed arrangement is shown and described in US. Patent 2,776,618 to Hartley. If desired, however, the electrode assembly may be employed with a suitable line storage memory device to produce line-by-line printing in which case skewing is unnecessary and a much higher printing speed can be achieved at the expense of more complex computer circuitry.

It will be noted that in FIG. 1 the image-receiving copy sheet 11 is backed by grounded electrode 14 and the pulse is applied to the character slug 13. It is only necessary that the powder carrying layer 12 be of insulating material to transmit the electric field of the character to the powder layer. Sheet llll can be either insulating or conductive in this embodiment. In FIGS. 2 to 5, however, since the pulse is applied to the backing electrode, such as 36, which is separated from the character face by both web 11 and the powder-carrying layer, such as 32, both the web and the powder-carrying layer must be insulating. If paper is used for web 11 it can be pre-conditioned prior to use by passing the web through an oven at to 200 degrees C. for a few seconds. This can be done immediately ahead of the recording station in the recording apparatus itself, or the web can be pre-dried, wound up and kept in a tight container until used. Papers which are impregnated with a plastic such as cellulose acetate or nitrate do not usually require such precautions.

It will also be appreciated that the copy sheet and the powder-carrying layer can be reversed in position relative to the character slug or drum, the polarities being correspondingly reversed, and the reading sense of the characters being changed to give a right-reading character on the copy sheet. In FIG. 1, of course, the copy sheet will in this event have to be insulating, while the powdercarrying layer can be either conductive or insulating. In FIGS. 2-5 both layers should be insulating as just explained.

The apparatus and methods of the present invention are, as is readily apparent, admirably suited for computer output and for other uses and application where high-speed printing is desired and particularly where an immediately visible record is useful. The printed record produced by the apparatus of the invention is immediately visible and available within a fraction of a second after image formation and can be produced at extremely high rates of character formation including rates at least as high as 20,000 characters per second. All of these advantages are achieved with electronic circuitry that is relatively simple in the computer art.

It is apparent that numerous variations and modifications may be made in the methods and apparatus of the invention in accordance with the needs of the particular use or application. The invention is, therefore, illustrated by, but not limited to, the scope of the specific disclosure.

What is claimed is:

l. A device for recording alphanumeric images which comprises, in combination, a character drum carrying a series of rings of conductive characters having their faces lying in a cylindrical formation, a thin cylinder of insulat ing material at least partly surrounding said formation and spaced from said faces by short air gaps, means for applying a layer of electrically charged powder to the outside of said insulating cylinder, means for advancing a web of sheet material against said insulating cylinder and in an are around said cylinder and then away from said cylinder and for simultaneously rotating said cylinder at the same peripheral velocity as said web, a series of curved elec trodes behind the position of the curved portion of said web, one electrode being opposite each of said character rings, means for rotating said character drum, and means to apply a timed voltage pulse of short duration to each of said electrodes to produce a silent electric discharge between selected character faces and the inside of said insulating cylinder to produce an electrostatic image on said insulating cylinder and transfer the afiinity of part of said powder layer to said web of sheet material.

2. Means for recording alphanumeric images in a few microseconds comprising, in combination, an electrode, a conductive character face, means to support said character face in closely spaced parallel relationship with the surface of said electrode with a pair of sheets disposed between said character face and said electrode, said sheets being in face-to-face contact, the sheet adjacent to said character face being of insulating material and being spaced from said character face by a short gap of from about one to about five mils, one of said sheets carrying a layer of electrostatically adhering powder on its face, said layer being sandwiched between said sheets, and means to apply an intense electric field of short duration between said character face and said sheet adjacent to said character face of sufficient magnitude to produce a silent electric discharge between said character face and said last-mentioned sheet and of a polarity to transfer the powder of at least a portion of said powder layer corresponding to the shape of said conductive character face from the sheet to which it is initially adhering to the other of said sheets.

3. A device for recording alphanumeric images in a few microseconds comprising, in combination, a printing station including an electrode, a conductive alphanumeric character face and means to support said character face in closely spaced relation with the surface of said electrode, a first means to advance into the printing station a print receiving web and a second advancing means simultaneously to advance into face-to- 10 face relationship with the print receiving web a developer web having releasable electrostatically charged powder on the facing surface thereof sandwiched between said webs, said powder having an affinity for said developer web, said electrode and said conductive alphanumeric character face being positioned with respect to each other and with respect to said print receiving web and said developer web so that said conductive alphanumeric character face is less than about 10 mils from said developer web and means to apply an intense electric field between said character face and said electrode of a magnitude sufficient to produce a silent electric discharge between said character face and said electrode, said field being of a polarity to transfer the portion of said powder opposite said character face to said print-receiving web and thereby produce a developed electrostatic image on said layer.

4. A high speed electrostatic printing apparatus capable of recording incoming information received at random in a few microseconds, said apparatus comprising a rotary character drum having a bank of like character rings thereon, each ring containing a series of electrically conductive character-shaped elements in a circumferential arrangement, the respective characters in a series being representative of different values of incoming information, means to rotate said drum at a constant angular velocity, a first moveable web of insulating material disposed tangentially relative to said drum, a second moveable web of insulating material disposed tangentially relative to said drum, said first web and said second web being contiguous with each other at their drum, the closest of said webs being less than about 10 mils from said drum at said point of tangency, a uniform layer of electrostatically charged marking particles adhering to said second web and sandwiched between said webs, an array of fixed electrodes disposed opposite to the web at positions corresponding to those of the ring there-opposite, means responsive to the value of incoming information to supply sequentially a voltage pulse to said electrodes when the selected ring character representative of said value is in angular alignment with said electrode, said voltage pulse being of a magnitude sufi'icient to initiate an ionizing field discharge between said selected ring character and the fixed electrode opposite it and being of a polarity to transfer a portion of said charged marking particles corresponding to the shape of said pulsed character electrode from said second web to said first web whereby the powder electrostatically adhering to said second web is deposited on said first web in image configuration and means to control said sequential means to shift said pulse to the next electrode after each recording operation.

5. A method of electrostatic recording which comprises, placing a charged powder layer electrostatically adhering to an insulating developer web against a recording web to form a sandwich, placing said sandwich between a backing electrode spaced opposite a print electrode shaped in the form of a symbol to be reproduced, said electrodes being positioned relative to each other to include a gap of from about one to about five mils between said sandwich and at least one of said electrodes, and transferring powder in the configuration of said print electrode by applying an electrical potential of a duration as short as a few micro-seconds across said electrodes, said potential being of a magnitude suflicient to initiate an ionizing field discharge between said electrodes and said sandwich and said potential being of a polarity to cause electrostatic transfer of said powder configuration from said developer web to said recording web forming a recording on said recording web.

6. A method of electrostatic recording which comprises covering a surface of an insulating developer web with a charged powder layer having an aflinity for said developer web surface, placing a recording web in contact with said powder layer to form a sandwich, placing said sandwich point of tangency relative to said in a printing gap formed by at least one backing electrode spaced opposite a rotating cylinder bearing a series of electrically conductive, alphanumeric, character faces, said sandwich being placed in said gap so that a space of from about one to about five mils exists between said sandwich and the periphery of said rotating cylinder, moving said sandwich relative to said printing gap and applying a voltage pulse as short as a few microseconds between said backing electrode and said cylinder, the time of application of said pulse being selected in accordance with coded electrical input signals so that said pulse occurs at a time in the rotation of said cylinder when a preselected character is adjacent said sandwich, said voltage pulse being sufiicient to initiate an ionizing field discharge between said selected conductive character and said sandwich and being of a polarity to transfer said powder opposite the end surface of said selected character from said developer web to said recording web forming a recording of said character shape.

i. 2 References Cited by the Examiner UNITED STATES PATENTS 2,248,522 7/41 Conrad. 2,633,796 4/53 Petri'ck. 7 2,715,360 8/55 Brown 101-426 2,764,500 9/56 Huebner. 2,771,336 11/56 MacGrifi. 2,777,745 1/57 McNaney. 2,787,952 4/57 Roche. 2,805,620 9/57 Rosen et al. 7 2,838,997 6/58 Monchicfi-Yeate s 101- 426 2,901,374 8/ 59 'Grandlach. 2,910,351 10/59 SZp ak et al.

FOREIGN PATENTS 734,909 8 /55 Great Britain; 745,500 2/ 5 6 Great Britain.

WILLIAM B. PENN, Primary Examiner. 

5. A METHOD OF ELECTROSTATIC RECORDING WHICH COMPRISES, PLACING A CHARGED POWER LAYER ELECTROSTATICALLY ADHERING TO AN INSULATING DEVELOPER WEB AGAINST A RECORDING WEB TO FORM A SANDWICH, PLACING SAID SANDWICH BETWEEN A BACKING ELECTRODE SPACED OPPOSITE A PRINT ELECTRODE SHAPED IN THE FORM OF A SYMBOL TO BE REPRODUCED, SAID ELECTRODES BEING POSITIONED RELATIVE TO EACH OTHER TO INCLUDE A GAP OF FROM ABOUT ONE TO ABOUT FIVE MILES BETWEEN SAID SANDWICH AND AT LEAST ONE OF SAID ELECTRODES, AND TRANSFERRING POWDER IN THE CONFIGURATION OF SAID PRINT ELECTRODE BY APPLYING AN ELECTRICAL POTENTIAL OF A DURATION AS SHORT AS A FEW MICROSECONDS ACROSS SAID ELECTRODES, SAID POTENTIAL BEING OF A MAGNETITUDE SUFFICIENT TO INITIATE AN IONIZING FIELD DISCHARGE BETWEEN SAID ELECTRODES AND SAID SANDWICH AND SAID POTENTIAL BEING OF A POLARITY TO CAUSE ELECTROSTATIC TRANSFER OF SAID POWER CONFIGURATION FROM SAID DEVELOPER WEB TO SAID RECORDING WEB FORMING A RECORDING ON SAID RECORDING WEB. 